package com.laz.knowledge.thirtyeight;

import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Signature;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

public class DSACoder extends Coder {  
		  
	    public static final String ALGORITHM = "DSA";  
	  
	    /** 
	     * 默认密钥字节数 
	     *  
	     * <pre> 
	     * DSA  
	     * Default Keysize 1024   
	     * Keysize must be a multiple of 64, ranging from 512 to 1024 (inclusive). 
	     * </pre> 
	     */  
	    private static final int KEY_SIZE = 1024;  
	  
	    /** 
	     * 默认种子 
	     */  
	    private static final String DEFAULT_SEED = "0f22507a10bbddd07d8a3082122966e3";  
	  
	    private static final String PUBLIC_KEY = "DSAPublicKey";  
	    private static final String PRIVATE_KEY = "DSAPrivateKey";  
	  
	    /** 
	     * 用私钥对信息生成数字签名 
	     *  
	     * @param data 
	     *            加密数据 
	     * @param privateKey 
	     *            私钥 
	     *  
	     * @return 
	     * @throws Exception 
	     */  
	    public static String sign(byte[] data, String privateKey) throws Exception {  
	        // 解密由base64编码的私钥  
	        byte[] keyBytes = decryptBASE64(privateKey);  
	  
	        // 构造PKCS8EncodedKeySpec对象  
	        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);  
	  
	        // KEY_ALGORITHM 指定的加密算法  
	        KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);  
	  
	        // 取私钥匙对象  
	        PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);  
	  
	        // 用私钥对信息生成数字签名  
	        Signature signature = Signature.getInstance(keyFactory.getAlgorithm());  
	        signature.initSign(priKey);  
	        signature.update(data);  
	  
	        return encryptBASE64(signature.sign());  
	    }  
	  
	    /** 
	     * 校验数字签名 
	     *  
	     * @param data 
	     *            加密数据 
	     * @param publicKey 
	     *            公钥 
	     * @param sign 
	     *            数字签名 
	     *  
	     * @return 校验成功返回true 失败返回false 
	     * @throws Exception 
	     *  
	     */  
	    public static boolean verify(byte[] data, String publicKey, String sign)  
	            throws Exception {  
	  
	        // 解密由base64编码的公钥  
	        byte[] keyBytes = decryptBASE64(publicKey);  
	  
	        // 构造X509EncodedKeySpec对象  
	        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);  
	  
	        // ALGORITHM 指定的加密算法  
	        KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);  
	  
	        // 取公钥匙对象  
	        PublicKey pubKey = keyFactory.generatePublic(keySpec);  
	  
	        Signature signature = Signature.getInstance(keyFactory.getAlgorithm());  
	        signature.initVerify(pubKey);  
	        signature.update(data);  
	  
	        // 验证签名是否正常  
	        return signature.verify(decryptBASE64(sign));  
	    }  
	  
	    /** 
	     * 生成密钥 
	     *  
	     * @param seed 
	     *            种子 
	     * @return 密钥对象 
	     * @throws Exception 
	     */  
	    public static Map<String, Object> initKey(String seed) throws Exception {  
	        KeyPairGenerator keygen = KeyPairGenerator.getInstance(ALGORITHM);  
	        // 初始化随机产生器  
	        SecureRandom secureRandom = new SecureRandom();  
	        secureRandom.setSeed(seed.getBytes());  
	        keygen.initialize(KEY_SIZE, secureRandom);  
	  
	        KeyPair keys = keygen.genKeyPair();  
	  
	        DSAPublicKey publicKey = (DSAPublicKey) keys.getPublic();  
	        DSAPrivateKey privateKey = (DSAPrivateKey) keys.getPrivate();  
	  
	        Map<String, Object> map = new HashMap<String, Object>(2);  
	        map.put(PUBLIC_KEY, publicKey);  
	        map.put(PRIVATE_KEY, privateKey);  
	  
	        return map;  
	    }  
	  
	    /** 
	     * 默认生成密钥 
	     *  
	     * @return 密钥对象 
	     * @throws Exception 
	     */  
	    public static Map<String, Object> initKey() throws Exception {  
	        return initKey(DEFAULT_SEED);  
	    }  
	  
	    /** 
	     * 取得私钥 
	     *  
	     * @param keyMap 
	     * @return 
	     * @throws Exception 
	     */  
	    public static String getPrivateKey(Map<String, Object> keyMap)  
	            throws Exception {  
	        Key key = (Key) keyMap.get(PRIVATE_KEY);  
	  
	        return encryptBASE64(key.getEncoded());  
	    }  
	  
	    /** 
	     * 取得公钥 
	     *  
	     * @param keyMap 
	     * @return 
	     * @throws Exception 
	     */  
	    public static String getPublicKey(Map<String, Object> keyMap)  
	            throws Exception {  
	        Key key = (Key) keyMap.get(PUBLIC_KEY);  
	  
	        return encryptBASE64(key.getEncoded());  
	    }  
}
